Method of transmitting telegraphic signals



H. B. R. BOOSMAN EIAL ,6 7

2 Shets-Sheet 1 JIM W; AMPLIFIER TRANSMITTER FIG.

INVENTORS HERMAN BERNARD RUDOLF BOOSMAN TJISKE DOUMA KLAAS PSZTHUMUS BY1%,1 A ENT METHOD OF TRANSMITTING TELEGRAPHIC SIGNALS March 15, 1949.

Filed July 15, 1946 JUL March 15, 1949.

Filed July 15, 1946 H. a. R. BOOSMAN EIAL 2,464,667

METHOD OF TRANSMITTING TELEGRAPHIC SIGNALS 2 Sheets-Sheet 2 AMPLIFIERTRANSMITTER FIG , TRANSFER RECEIVER oswcs 6 HERMAN BERNARDYRUDOLFINVENTO S BOOSMAN TJISKE DOUMA KLj AS PiSTHUMU 'Agt m Patented Mar. 15,1949 METHOD OF TRANSMITTING TELE- GRAPHIC SIGNALS Herman Bernard RudolfBoosman,

and Klaas Posthumus, Eindhovcn,

Tjlske Douma,

Netherlands,

assignors to Hartford National Bank and Trust Company, Hartford, Conn.,

as trustee Application July 15, 1946, Serial No. 683,59;

In the Netherlands June 24, 1943 Section 1, Public Law 690, August a,1946 Patent expire! June 24; 19.63

20 Claims. (01. 250-8) This invention relates to a method oftransmitting telegraphic signals and also to transmitting and reecivingdevices arranged for the transmission and reception respectively ofsignals emitted by this method.

According to the invention, the mean energy required for thetransmission is materially reduced .by transmitting one or more pulsesof substantially constant length of time at the beginning and in somecases at the end of each signal to be transmitted, either the pulses atthe beginning of several signals or the pulses at the end and thebeginning of the same signal having a difiering time nature.

A further advantage of the method according to the invention consists inthat the signal hiss ratio occurring in the receiver can be raisedconsiderably over the signal hiss ratio obtainable in the usualtransmission of telegraphic signals, the mean transmission energy beingotherwise the same.

In order that the invention may be clearly understood and readilycarried into effect it will now be described more fully with referenceto the accompanying drawing.

The figures of the drawing are as follows:

Fig. 1 is a pattern of the telegraph signals to be transmitted,

Fig. 2 is a schematic diagram of a preferred embodiment of a transmitterfor emitting pulses of the type shown in line b of Fig. 1,

Fig. 3 is a pattern illustrating various pulses generated in thetransmitter of Fig. 1,

Fig. 4 is a schematic diagram of another preferred embodiment of atransmitter,

Fig. 5 is a schematic diagram of a receiver for the reception of pulsesof the type shown in line 41 of Fig. 1, and

Fig. 6 is a schematic diagram of a pulse generator for use in connectionwith a receiver of the type shown in Fig. 5.

Figure 1 shows a telegraphic signal to be transmitted made up of a dash,a dot and a dash. The energy required for the transmission of the signalis proportional to the cross-hatched surface areas. For enabling thetransmission of this energy a transmitter of definite power is requiredand this power must be such that the mean energy to be transmitted pertime unit, or in other words the contents of the cross-hatched surfacesdivided by the time T, can be coped with by the transmitter withoutoverloading.

According to the invention, the telegraphic signals as shown in Figure1a are transmitted by means of pulses of constant length of time, for.

example of the nature shown in Figure 1b, 10 or Id. In the case of thepulse nature shown in Figure 117 two short successive pulsesjare emittedat the beginning of each signal, whereas the end of each signal isdenoted by a single pulse. In the case of the pulse nature shown inFigure 1c the beginning of each dash is represented by two pulses, thebegimiing of each dot and the end of both dashes and dots. by a singlepulse. The

pulse nature shown in Figure 1d essentially corresponds with the natureshown in Figure 1c, the

difference being that the pulses at the end of the telegraphic signalsare emitted.

As before, the energy required for the transmission of pulses of thenature shown in the Fi ures 1b, 1c and 1d is decided by the surface areaof the pulses. This energy is materially lower than the energy requiredfor the transmission of the signals shown in Figure 1a. The same remarkapplies to the mean energy. The'use of a transmitter of identical powertherefore permits oi the pulses shown in Figures 117, 1c and 1d beingemitted with considerably larger amplitudes and with greater steepness.This ensures a more favourable signal hiss ratio on the receiver sidethan in the case of transmitting the signals shown in Figure 1a,particularly if receivers sensitive to the flank steepness are used.

Figure 2 shows a transmitter device for emitting pulses of the natureshown in Figure 11) by wireless telegraphy. This transmitting devicecomprises a key I, a device 2 for the conversion of telegraphic signalsinto pulses of the nature shown in Figure 111, an amplifier 3 and atransmitter 4, in which a carrier wave is so modulated by the amplifiedpulses that carrier wave pulses are obtained, and in addition an aerial5 by which the high-frequency oscillations are emitted.

At the beginning of a dash to be transmitted the key I is moved to theleft with the result that a condenser 6 becomes charged across aresistance 1 until the starting-up voltage of a gridcontrolled gaseousdischarge tube 8 is reached. At this moment the condenser E. is suddenlydischarged across the tube 8 with the result that a pulse-like voltageas represented in Figure 3 by the impulse Ill is set up across aresistance 9 in the cathode lead of the tube 8. Concurrently with thecharging of the condenser 6 a condenser ll becomes charged across aresistance l2. Due to the fact that the time constant of the chargingcircuit of the condenser ll exceeds that of the charging circuit of thecondenser 6, the start-. ing-up voltage of the grid-controlled gaseousdischarge tube It is reached slightly later than the 3 starting-upvoltage of the tube 0. The startingup of the tube I3 brings about asudden discharge of the condenser II with the result that as before apulse is set up across the resistance said pulse being designated I4 inFigure 3 and occurring slightly later than the pulse I0.

At the end of the dash the key is moved to the right with the resultthat a condenser I5 becomes charged via a resistance I0 and, as thestartingup voltage of a grid-controlled gaseous discharge tube I8 isreached, gets discharged across this tube and sets up a pulse across theoutput resistance 9. This pulse is designated I1 in Figure 3.

At the beginning of the next signal two pulses I0 and I9 are set up insuccession in an identical manner, whereas at the end of the signal asingle pulse is obtained.

The pulses obtained in succession across the resistance 8 are causedafter amplification by an amplifier sin the transmitter I to modulate acarrier wave.

In the embodiment described, the grid circuits of the tubes 0, I0 and I6include a common source of bias. If the bias voltages of the tubes 8, I3and I0 are made singly variable the starting-up voltages can be soadjusted that the pulses generated by the tubes have an identicalabsolute height.

The device described also permits of settingup pulses of the natureshown in Figure 1d. In this case it is, however, necessary for the key Ito be arranged so as to be moved into the lefthand position for settingup dashes, into the righthand position for setting up dots and to occupyan intermediate position of equilibrium in the intervals between thesignals.

It is not essential that the tubes 8, I3 and I 6 should be constitutedby grid-controlled gaseous discharge tubes. It is directly possible touse standard neon tubes in the circuit described but in this case thestarting-up voltage is no longer adJustable. In addition, the value ofthe voltage pulse across the output resistance is decided approximatelyby the difierence between the starting-up and the operating voltages ofthe tubes. In this case, the amplitude of the voltage pulses set up istherefor generally smaller and amplification of the pulses before theyare fed to the transmitter will be necessary.

In practice it has been found that in the use of neon tubes a commonoutput resistance 9 in the cathode lead of the tubes does not involveany difficulty. In the use of grid-controlled gaseous discharge tubes itis desirable to employ the circuit arrangement shown in Figure 4. Inthis case, relative influencing of the tubes 8, I3 and I 8 is avoided byincluding a separate resistance 2|, 22 and 23 respectively in thecathode lead of each of the tubes and the feeding the voltages set upacross these resistances via decoupling resistances 24, 25 and 26respectively to a common output resistance 21.

A device for the reception of pulses of the nature shown in Figure 1a isshown in Figure 5, the oscillations received in the aerial I00 being ledto a receiver IGI which is arranged in the usual manner and in whichafter detection pulses of the nature shown in Figure 1b are set up.These pulses are fed, in some cases via'a transfer device I02, later tobe more fully described, to a device I03 which serves for the conversionof pulses into telegraphic signals. The telegraphic signals set up inthe output circuit of the device I03 are fed to a reproduction deviceare.

The device I 03 comprises two discharge tubes I05 and I08, the anodecircuit of one tube being connected to the grid circuit of the othertube, as in the case oi. the well-known kalirotron circuit arrangementwhich, as is well-known, has two positions of equilibrium in whicheither the tube I05 allows the passage of current and the tube I06 isblocked or conversely.

In the oil position the tube I00 allows current to pass and the tube I00is disrupted. If the pulses received are then fed to the grid oi. thetube I00, as shown in the figure, and this is effected in such mannerthat the grid of the tube becomes more positive, the circuit continuesoccupying the said position of equilibrium. In order to ensure that onreception of two associated pulses at the beginning of each signal thecircuit passes to the other position of equilibrium, 9. tube I01 isconnected in parallel with the tube I00 and has the received pulses fedto it via a resistance I08. In addition, a condenser I I0 shunted by avery high resistance I00 is interconnected between the grid and thecathode of the tube I01. In the of! position, the tube I01 is disruptedby means of a source of bias III. The time constant of the integratingnetwork formed by the elements I00, I09 and H0 is chosen to be such thatonly after reception of two pulses in quick succession the voltage setup by the pulses across the condenser 0 has increased to such an extentthat the negative bias of the tube I01 is balanced at least in part andthe tube I01 is rendered conductive. As soon as anode current passes inthe tube I01 a voltage drop is set up across a resistance II2, which isincluded in the grid circuit of the tube I06 and puts this tube out ofoperation, the tube I05 becoming thus conductive.

At the beginning of the second of two associated pulses a voltage dropis consequently set up across a resistance I I3 in the cathode lead ofthe tube I05, said voltage drop subsisting until under the influence ofthe single pulse received at the end of the signal the tube I06 is againrendered conductive so that the tube I05 is disrupted. Thus, telegraphicsignals are consequently received across the resistance I I3 and are fedto the reproduction device It.

In order to secure a stable operation of the device I03 it is desirablethat the pulses fed to the latter should have identical amplitude at alltimes. For this purpose, provision is made for a device I02, which isconstituted for example by a limiter. Preferably, however, it isconstituted by a device for generating pulses which is normallydisrupted and is governed by the pulses received.

One form of construction of such a device is shown in Figure 6. Thedevice concerned is constituted by a relaxation generator comprising acondenser H4 which can be charged across a resistance H5 and can bedischarged across a relay tube IIG, each time the grid of the tube II6has fed to it a received pulse. At each dis charge of the condenser apulse-like voltage can be obtained via a resistance II1 included in thecathode lead.

In order to prevent disturbances which are set up between the pulses-andwhose amplitude is of pulses corresponding said mark signals, the

wave radio telegraphy signals of the mark-space type, comprising thesteps of converting the mark signals into pulse signals of substantiallyconstant duration and spaced in time corresponding to the duration ofsaid mark signals, the pulse signals corresponding to the initiation ofsaid mark signals being different in number from those corresponding thethe termination thereof, transmitting said pulse signals through space,receiving said signals, and converting said pulse signals back to saidmark signals thereby reproducing said telegraphy signals.

2. A method of communicating by continuous wave radio telegraphy signalsof the mark-space type, comprising the steps of converting the marksignals into pulse signals comprising a pair of pulses corresponding tothe initiation or said mark signals and a single pulse corresponding tothe termination of said mark signals, transmitting said pulse signalsthrough space, receiving said pulse signals, and converting saidreceived pulse signals back to said mark signals thereby reproducingsaid telegraphy signals.

3. A method of communicating by continuous wave radio telegraphy signalsof the dot-spacedash type, comprising the steps of converting the dotsignals into pulse signals comprising a single pulse corresponding tothe initiation and termination of said dot signals and converting thedash signals into pulse signals comprising a. pair to the initiation ofsaid dash signal and a single pulse corresponding to the termination ofsaid dash signal, transmitting said pulse signals through space,receiving said pulse signals, and converting said received pulse signalsback to said dot-space-dash signals thereby reproducing said telegraphysignals.

4. A method of communicating by continuous wave radio telegraphy signalsof the dot-anddash type, comprising the steps of converting the dotsignals into pulse signals comprising a single pulse corresponding tothe initiation of said dot signals and converting the dash signals intopulse signals comprising a pair of pulses corresponding to theinitiation of said dash signals, transmitting said pulse signals throughspace, receiving said pulse signals, and converting said received pulsesignals back to said dot-and-dash signals thereby reproducing saidtelegraphy signals.

5. Apparatus for communicating by means of continuous wave radiotelegraphy signals of themark-space type, comprising a gaseous dischargetube device to convert the mark signals into pulse signals ofsubstantially constant duration and spaced in time corresponding to theduration of pulse signals corresponding to the initiation of said marksignals being different in number from those. corresponding to thetermination thereof, means to transmit said pulse signals through space,means to receive said transmitted pulse signals, and a second dischargetube device to convert said pulse signals back to said mark signalsthereby to reproduce said telegraphy signals.

6. Apparatus for communicating by means of continuous wave radiotelegraphy signals of the mark-space type, comprising a gaseousdischarge tube device to convert the mark signals into pulse signalscomprising a pair of pulses corresponding to the initiation of the marksignals and a single pulse corresponding to the termination of said marksignals, means to transmit said pulse signals through space, means toreceive said transmitted pulse signals, and a second discharge tubedevice to convert said pulse signals back to said mark signals therebyto reproduce said telegraphy signals.

7. Apparatus for communicating by means of continuous wave radiotelegraphy signals of the dot-and-dash type, comprising a gaseousdischarge tube device to convert the dot signals into pulse signalscomprising a single pulse and to convert the dash signals into pulsesignals comprising a pair of pulse signals through space, means toreceive said transmitted pulse signals, and a second discharge tubedevice to convert said pulse signals back to said mark signals therebyto reproduce said telegraphy signals,

8. Apparatus for communicating by means of continuous wave radiotelegraphy signals of the dot-and-dash type, comprising a gaseousdischarge tube device to convert the dot signals into pulse signalscomprising single pulses corresponding to the initiation and terminationof said dot signals and to convert the dash signals into pulse signalscomprising a pair of pulses corresponding to the initiation of said dashsignals and a single pulse corresponding to the termination thereof,means to transmit said pulse signals through space, means to receivesaid transmitted pulse signals, and a second discharge tube device toconvert said pulse signals back to said mark signals thereby toreproduce said telegraphy signals.

9. Apparatus for keying a continuous wave transmitter for radiotelegraphy transmission of the mark-space type wherein the initiationand termination of each mark signals is represented by a differentnumber of pulses of substantially constant duration, said duration beingshort in comparison to the duration of said mark signal, comprising aplurality of capacitors, each of said capacitors having a chargingcircuit and a discharging circuit, the discharging circuit of at leastone of said plurality of capacitors having a time constant difierentfrom the remainder of said capacitors, means responsive to theinitiation of said mark signal simultaneously to charge a given numberof said plurality of capacitors, means to discharge said given number ofsaid plurality of capacitors across the discharging circuit thereof,means responsive to the termination of said mark signal to charge adifferent number of capacitors, means to discharge said different numberof capacitors across the discharging circuit thereof, and means toconnect the discharging circuits of said capacitors to said transmitter.

10. Apparatus for keying a continuous wave transmitter for radiotelegraphy transmission of the mark-space type wherein the initiationand termination of each mark signal is represented respectively by apair of pulses and a single pulse of substantially constant duration,comprising a first, a second and a third capacitor, each of saidcapacitors having a charging circuit and a discharging circuit, thedischarging circuits of said first and said second capacitors havingdifferent time constants, means responsive to the initiation of saidmark signal simultaneouslyuto charge said first and said secondcapacitors} means to discharge said capacitors in succession across thedischarging circuits thereof, means responsive to the termination ofsaid mark signal to close the charging circuit of said third capacitor,means to discharge said third capacitor across the discharging circuitthereof,

pulses, means to transmit said and means to connect the dischargingcircuits of said capacitors to said transmitter.

11. Apparatus for keying a continuous wave transmitter for radiotelegraphy transmission of the dot-and-dash type wherein the initiationand termination of each dot signal is represented respectively by asingle pulse and the initiation and termination of each dash signal isrepresented by a pair of pulses and a single pulse of substantiallyconstant duration, comprising a first, a second and a third capacitor,each of said capacitors having a charging circuit and a dischargingcircuit, the discharging circuits of said first and said secondcapacitors having difierent time constants, means responsive to theinitiation of said dash signal to close the charging circuits of saidfirst and said second capacitors simultaneously to charge said first andsaid second capacitors, means to discharge said capacitors in successionacross the discharging circuits thereof, means responsive to thetermination of said dash signal to close the charging circuit of saidthird capacitor, means responsive to the inititation and termination ofsaid dot si nal to charge said third capacitor, means to discharge saidthird, capacitor across the discharging circuit thereof, and means toconnect the discharging circuits of said capacitors to said transmitter.

12. Apparatus for keying a continuous wave transmitter for radiotelegraphy transmission of the dot-and-dash type wherein the initiationof each dot signal is represented respectively by a single pulse and theinitiation of each dash signal is represented by a pair of pulses ofsubstantially constant duration, comprising a first, a second and athird capacitor, each of said capacitors having a charging circuit and adischarging circuit, the discharging circuits of said first and saidsecond capacitors having different time constants, means responsive tothe initiation of said dash signal to close the charging circults ofsaid first and said second capacitors simultaneously to charge saidfirst and said second capacitors, means to discharge said capacitors insuccession across the discharging circuits thereof, means responsive tothe initiation of said dot signal to close the charging circuit of saidthird capacitor, means to discharge said third capacitor across thedischarging circuit thereof, and means to connect the dischargingcircuits of said capacitors to said transmitter.

13. Apparatus for keying a continuous wave transmitter for radiotelegraphy transmission of the mark-space type wherein the initiationand termination of each mark signal is represented respectively by apair of pulses and a single pulse of substantially constant duration,comprising a first, a second, and a third capacitor, each of saidcapacitors having a charging circuit and a discharging circuitcomprising a gaseous discharge transmitter for radio telegraphytransmission of "the mark-space type wherein the initiation and tube anda resistor, the discharging circuits of said first and said secondcapacitors having different time constants, means responsive to theinitiation of said mark signal to close the charging circuits of saidfirst and said second capacitors simultaneously to charge said first andsaid second capacitors, means comprising the gaseous discharge tubes ofthe respective discharging circuits to discharge said capacitors insuccession across said resistor, means responsive to the termination ofsaid mark signal to close the charging circuit of said third capacitorto charge said capacitor, means comprising the gaseous discharge tube ofthe respective discharging circuit to distermination of each mark signalis represented respectively by a pair of pulses and a single pulse ofsubstantially constant duration, comprising a first, a. second and athird capacitor, each of said capacitors having a charging circuit and adischarging circuit comprising a grid-controlled gaseous discharge tubeand a discharging resistor, the discharging circuits of said first andsaid second capacitors havin different time constants, means responsiveto the initiation of said mark signal to close the charging circuits ofsaid first and said second capacitors simultaneously to charge saidfirst and said" second capacitors. means comprising the respectivegrid-controlled gaseous discharge tube of said discharging cir-.

cuits to discharge said first and said second capacitors in successionacross the discharging resistors of the respective discharging circuits,means responsive to the termination of said mark signal to close thecharging circuit of said third capacitor to charge said third capacitor,means comprising the respective grid-controlled gaseous discharge tubeto discharge said third capacitor across the discharging resistor of therespective discharge circuit, and means to connect the dischargingcircuits of said capacitors to said transmitter.

15. Apparatus for keying a continuous Wave transmitter for radiotelegraphy transmission of the mark-Space type wherein the initiationand termination of each mark signal is represented respectively by apair of pulses and a single pulse of substantially constant duration;comprising a first, a second and a third capacitor, each of saidcapacitors having a charging circuit and a discharging circuit, saiddischarging circuits comprising a grid-controlled gaseous discharge tubefor each of the respective capacitors coupled to a common dischargingresistor, the discharging circuits of said first and said secondcapacitors having difierent time constants, means responsive to theinitiation of said mark signal to close the charging circuits of saidfirst and said second capacitors simultaneously to charge said first andsaid second capacitors, means comprising the respective grid-controlledgaseous discharge tube of said discharging circuits to discharge saidfirst and said second capacitors in succession across said commondischarging resistor, means responsive to the termination of said marksignal to close the charging circuit of said third capacitor to chargesaid third capacitor, means comprising the respective grid-controlledgaseous discharge tube to discharge said third capacitor across saidcommon discharging resistor, and means to connect said dischargingresistor to said transmitter.

16. Apparatus for keying a continuous wave transmitter for radiotelegraphy transmission of the mark-space type wherein the initiationand termination of each mark signal is represented respectively by apair of pulses and a single pulse of substantially constant duration,comprising a first, a second and a third capacitor, each of saidcapacitors having a charging circuit and a discharging circuitcomprising a grid-controlled gaseous discharge tube, a coupling resistorand a discharging resistor, the discharging circuits of said first andsaid second capacitors having diflerent time constants, means responsiveto the initiation of said mark signal to close the charging circuits ofsaid first and said second capacitors simultaneously to charge saidfirst and said second capacitors, means comprising the respectivegrid-controlled gaseous discharge tube of said discharging circuits todischarge said first and said second capacitors in succession across thedischarging resistors of the respective discharging circuits, meansresponsive to the termination of said mark signal to close the chargingcircuit of said third capacitor to charge said third capacitor, meanscomprising the respective gridcontrolled gaseous discharge tube todischarge said third capacitor across the discharging resistor of therespective discharge circuit, and I means comprising said couplingresistors to couple said discharging resistors to said transmitter. 1'7.Apparatus for receiving continuous wave radio telegraphy signals of themark-space typewherein the initiation and termination of each marksignal is represented respectively by a difierent number of pulses ofsubstantially constant duration, comprising a first gaseous dischargetube having an input circuit and an output circuit, a second electrondischarge tubehaving an input circuit coupled to the output circuit ofsaid first electron discharge tube and an output circuit coupled to theinput circuit of said first electron discharge tube to render saidsecond tube conducting when said first tube is non-conducting andconversely to render said second tubenon-conducting when said first tubeis conducting, a. discharging circuit coupled to said first tube andbeing responsive only to the greater number of said pulses, means toapply said signals to the input circuit of said first tube, and meanscoupled to the output circuit of said second tube to reproduce saidsignals.

18. Apparatus for receiving continuous wave radio telegraphy signals ofthe mark-space type wherein the initiation and termination of each marksignal is represented respectively by a pair of pulses and a singlepulse of substantially constant duration, comprising a first electrondischarge tube having an input circuit and an output circuit, a secondelectron discharge tube having an input circuit coupled to the outputcircuit of said first electron discharge tube and an output circuitcoupled to the input circuit of said first electron discharge tube torender said second tube conducting when said first tube is nonconductingand conversely to render said second tube non-conducting when said firsttube is conducting, a discharging circuit coupled to said first tube andbeing responsive only to said pair of pulses, an integrating networkcoupled to the input circuit of said first tube, means to apply saidsignals to said integrating network, and means coupled to the outputcircuit of said second tube to reproduce said signals.

19. Apparatus for receiving continuous wave radio telegraphy signals ofthe mark-space type wherein the initiation and termination or each marksignal is represented respectively by pairs of pulses and a single pulseof substantially constant duration, comprising a first electrondischarge tube having an input circuit and an output circuit, a secondelectron discharge tube having an input circuit coupled to the outputcircuit of said first electron discharge tube and an output circuitcoupled to the input circuit of said first electron discharge tube torender said second tube conducting when said first tube is nonconductingand conversely to render said second tube non-conducting when said firsttube is conducting, a discharging circuit coupled to said first tube andbeing responsive only to said pairs of pulses, a pulse signal generatorcoupled to the input circuit of said first tube, means to apply saidsignals to said pulse signal generator, and means responsive to theoutput of said second tube to reproduce said signals.

20. Apparatus for receiving continuous wave radio telegraph signals ofthe mark-space type wherein the initiation and termination of each marksignal is represented respectively by pairs of pulses and a single pulseof substantially constant duration, comprising a first electrondischarge tube having an input circuit and an output circuit, a secondelectron discharge tube having an input circuit coupled to the outputcircuit of said first electron discharge tube and an output circuitcoupled to the input circuit of said first electron discharge tube torender said second tube conducting when said first tube is nonconductingand conversely to render said second tube non-conducting when said firsttube is conducting, a discharging circuit coupled to said first tube andbeing responsive only to said pairs of pulses, a pulse signal generatorcoupled to the input circuit of said first tube and being responsiveonly to signals having an amplitude above a predetermined thresholdvalue, means to apply said signals to said pulse signal generator, andmeans responsive to the output of said second tube to reproduce saidsignals.

HERMAN BERNARD RUDOLF BOOSMAN. TJISKE DOUMA. miss POSTHUMUB.

REFERENCES crrm) The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 540,233 Great Britain Oct. 9, 194-1

